Slow-wave structure



Feb- 4, 1958 s. sENslPER SLOW-WAVE STRUCTURE Filed April` 5, 1955 United States Patent O 'ice Aircraft Company, Culver City, Calif., a corporation of Delaware Application April 5, 1955, Serial No. 499,330 6 Claims. (Cl. S15-13.5)

This invention relates to microwave tubes and( more particularly to a unidirectional wave propagation circuit fora traveling-wave tube. l

A traveling-wave tube generally comprises an evacuated envelope, `a slow-wave structnre, an electron gun for projecting an election stream through the slow-wave structure, and means Vfor producing a uniform axial magnetic field to focus or confine the stream. A slow-wave structure has recently been developed which may be used in conjunction with a relatively high-powered travelingwave tube amplifier. Such aslowwave structure is described and claimed Vin copending application Serial No. 450,987, entitled High-Power Microwave Tube, led

lAugust 18, 1954, by C. K. Birdsall.

Although well-known backward-wave self-oscillationis not a severely limiting Afactor in the use of suchslowwave structures, it is desirable that the amplitudes of reccted Wave regeneration and selfoscillation be kept at a minimum or eliminated. One solution to this problem is` described and claimed in copending application Serial No. 471,660, tiled November 29, 1954, bySam-uel Sensiper. It has been previouslysuggested vthat a yferromagnetic or ferrite helix be disposed adjacent-totheslowwave structure of a traveling-wave tube to attenuate backward or reflected waves propagatedin -a direction oppo-l :site to that of the electron stream fof the tube.

In such. a case, forward wave propagation is'substantiallyunattenuated. The unidirectional wave propagation properties of a 4ferromagnetic ferrite are well-known. A ferritehelix is sometimes used with a traveling-wave tube that employs a conductive helix for a-slow-wave structure. This isrequired because it is necessary to obtain an arcuately directed direct-current magnetic eldin a ferrite Ymember in applane transverse to the longitudinal axis of the traveling-wave tube slow-wave structure in order to achieve rthe desired non-reciprocalattenuation. Theferiite helix 'with the means which provides the confining axial magnetic field for theelectron stream is thus used to divert aportion ofthe magnetic tlux of the axial magnetic field fand to provide a transverse component of the magnetic 'eld. This is accomplished by'taking advantage of the fact that the `magnetic ux of the axial magnetic vfieldl tends to follow the relatively low reluctancehelical path provided by the ferrite helix.

Substantial reciprocal attenuation ie generally -encountered valong vcert'ainpor'tionsofthe length l o'fitlie slowwavezstructure of the above-'mentioned Birdsall application when a ferrite Vhelix is employed. Hence, the use of'a ferrite helix with such a high-powe slovvlwave structure is undesirable.

Itis therefore an obect of the invention to provide an improved unidirectionalV wave' propagation circuit for a traveling-wave tube. l

l Itis'v another object-"ofV the invention tofprfovide means for'seleetively atter'inating backward and reflected waves relatively fhi'glipowered travelingwave tube.

8225er VPatented Feb. 4, `1958 In the previously mentioned Birdsall application, a slow-wave structure is disclosed comprising a plurality of conductive rings having conductive means disposed between adjacent pairs of the conductive rings thereby to connect adjacent pairs of the conductive rings alternately at diametrically opposed points. In accordance with 'the present invention, an elongated 'ferromagnetic ferrite member is disposed degrees about the slow-wavestructure from the diametrically opposed lpoints where the rings 'are interconnected on at least one side of the slowwave structure. The ferrite members are disposed vin an axial plane and have a certain angle-of inclination with respect to a plane transverse tothe longitudinal axis of -the slow-wave structure. The use of ferrite material at the points where the conductive rings rare interconnected is thus avoidedand substantial reciprocal attenuation is prevented.

The novelfeatureswhic'h are believed to be characteristeric of the invention, both 'as to its organization and Vmethod of operation, together with further objects and advantages thereof, will be better understood from the following description considered .in connection with .the accompanying-drawing lin which an embodiment of the invention is illustratedby Way of example. It is to be expressly understoodfhowever, that the drawing is for the purpose Vof illustration and description only, and .isnot intended as a deiinition of the `limits of the invention.

Fig. 1 is a sectional view of atraveling-wave .tube incorporating one embodiment of the slow-wave structure of the present invention;

Fig. 2 is a sectional view taken 4on the line 2-2 in Fig. 1;

Fig. 3 is a section of the tube shown in Fig. 2 taken on line 3 3 of Fig. 2;

Fig. 4 is another section of the tube taken on line 4-4 in Fig. 2; and I Fig. 5.is an isometric, broken-away section of the slowwave structure of the traveling-wave'tube `of Fig. '1.

Referring to the drawing, a travelin'gw'aveftube 10 is shown in Fig. 1 comprising an elongated evacuated envelope 12 having an enlarged portion "14 'atits 'left end. Within the enlarged portion, an electron gun 1f6 is shown comprising a cathode 18 which is provided with 'a lilament 2n, focusing electrode 22, and an accelerating anode 24. One side of the lilament 20 Vis connected to a cathode as is the focusing electrode 22. Filament 20 is provided with a filament source of potential 26', the negative `side of which is reference to a potential considerably below ground by means of an accelerating source of potential 2 8, the positive terminal of which is connectedfto ground. Focusing electrode 22 is a frusto-conical electrode having an internal surface of revolution disposed ati an angle of 671/2 degrees from its axis of revolution. .Accelerating anode 24 is maintained at a potential somewhat positive with respect to cathode 18 by means of a connection to a tap 34 on accelerating source of potential 28.

In the direction of electron ilow from electron gun 16 within the envelope 12 there is shown a slow-wave structure 30 and at the right end of the lenvelope 12 a collector electrode 32 is provided.V Radio frequency Yor R. F. wave venergy is introduced' to the ktnbe 1u through a rectangular input waveguide 36 which 'has a vsnorted terminationv 38 and a conductive matching sleeve 40.

A rectangular R. F. output waveguide 42 is 'shown at the right end of the tube 10tdisposed about the right end of slow-wave structure 30 having a shorted termination 44 and a similar conductive sleeve 46 disposed about the envelope 12 .to prevent radiation of ele ctromagnetic energyY therefrom. Collector electrodezy is maintained at apbtential somewhat positive 4vvi'threspect to that f slow-wave structure A30 in order to prevent the ncol- 3 lecton of secondary electrons at slow-wave structure 30 produced by primary electrons from the beam developed by the gun 16 causing secondary emission at collector 32. To this end, a source of positive potential 48 is connected between collector' 32 and ground.

Slow-wave structure 30 is maintained at ground potential by an appropriate connection thereto as shown.

A plurality of ferromagnetic ferrite members 50 are shown disposed on one side of the slow-wave structure 30, another group of members are in fact disposed about the slow-wave structure 30 on the opposite side although they cannot be seen because of the particular broken A direct-current axial magsection taken in Fig. 1. netic eld is provided throughout the length of the tube by a solenoid 52 through which direct-current is passed by means of a source of potential 54. Solenoid 52.is employed to provide a direct-current magnetic field coaxially with the slow-wave structure 30 to focus or to confine the electron stream Vproduced by electron gun 16 and in addition to produce a magnetic field through the ferrite members 50 to provide the unidirectional atv tenuation characteristic of the slow-wave transmission path of the present invention.

The envelope 12 is shown in Fig. 2 with the slowwave structure V30 and the ferrite members 50 disposed tory'tube operation, it is unnecessary to position the ferrite members 50 at each of the conductive cylinders 130 ordirectly adjacent any of them. The position of a ferrite member 50 adjacent each of the conductive cylinders 130 Vas shown in Figs. 1 to 4 is not necessarily indicative of a position which will lead to optimum perfomance. Their position for optimum performance will generally be preferably obtained empirically. The algebraic sign of the vertical angle of inclination of the ferrite members 50 with respect to a plane transverse to Vthe axis of the slow-wave structure will be determined 4by the direction` of the axial magnetic `iield. Fig. 5 is an isometric broken-away sectional view of the slowwave structure 30 comprising the conductive rings 130 with the conductive connecting means or rods 132 disposed between adjacent pairs of the conductive cylinders alternately at diametrieally opposed points.

The ferrite members 50 may have a circular, triangular, rectangular, or square or other symmetrical or nonsymmetrical cross section depending upon the type and the amount of attenuation desired and their dielectric loading characteristics. They generally must be dis.

posed at a predetermined angle witha plane transverse to the axis of the slow-wave structure`30 in order that an arcuately directed or transversely directed magnetic field may be provided through the ferrite members 50. The existence of a ferrite member adjacent to or in the kneighborhood of the axially conductive segments 132 is'very undesirable in that the existence of a. ferromagnetic body in that position causes reciprocal attenuation in the waves propagated along the slow-wave structure 30. That is, in such a case, attenuation of forward l' waves would be produced in an amount about equal to that of backward and reflected waves. This is obviously undesirable.

It is to be noted that the ferrite members 5t) shown in Fig. 4 are disposed at a predetermined angle with respect to a plane transverse to the longitudinal axis of the slow-wave structure; however, the ferrite members shown in Fig. 3 are disposed at an angle opposite in algebraic sign of that of the ferrite members shown in Fig. 4. This relationship must be maintained between the ferrite members on opposite sides of the slow-wave structure because the axial magnetic field produced by the solenoid 52 will be unidirectional along the axis of the slow-wave structure 30. However, wave propagation about the rings 130 of the slow-wave structure 30 will be in opposite directions. For example, in Fig. 5 currents flowing in the direction shown by the arrow 150 will divide into two portions at the axially conductive segment 132 as indicated by the arrows 152 and 154. Currents ilowing according to the arrows 152 and 154 will thus be flowing in opposite arcuate directions. Since the magnetization of the ferrite members 50 will be in the same direction, the ferrite members on opposite sides of the rings 130 of the slow-wave structure 30 must thus be inclined with a plane transverse to the axis of the slow-wave structure 30 approximately at the same angle but in oppositedirections, that is, ferrite members 50 on the Aright side of the slow-wave structure 30 may be inclined ata forward angle as shown in Fig. 4 and the ferrite members on the left side of the slow-wave structure 30 may be inclined at a rearward angle as `indicated in Fig. 3.

What is claimed is: 1. In a traveling-wave tube, a substantially unidirectional wave propagation structure comprising a slowwave structure for propagating electromagnetic waves and having a longitudinal axis, said slow-wave structure including a plurality of `conductive rings having apertures disposed in register with each other along said axis, and conductive means disposed between adjacent pairs of said conductive rings connecting said adjacent pairs of said conductive rings alternately at diametrically opposed points, said conductive means lying substantially in a first plane which also includes said axis,

and anelongated ferromagnetic ferrite member disposed to at least one side of each of said conductive rings, said ferrite members on said one side of said conductive rings Vbeing disposed in a plane parallel to said first plane and each having a predetermined angle of inclination with respect to a plane transverse of said longitudinal axis of said slow-wave structure.

2. In a traveling-wave tube, a substantially unidirec- `tional wave propagation structure having a longitudinal axis and comprising a slow-wave structure propagating 'electromagnetic waves, said slow-wave structure including a plurality of conductive rings having apertures disposed along said longitudinal axis in register with each other, and conductive means disposed between adjacent --pairs of said conductive rings connecting said adjacent 'pairs vof `said conductive rings alternately at diametrically opposed points all lying substantially within a first plane containing said longitudinal axis, and an elongated ferromagnetic ferrite member disposed along each vside of each of said conductive rings, said ferrite members being disposed in two planes parallel to said first plane and having predetermined angles of inclination with respect to a plane'transverse to said longitudinal axis,

said ferrite members on one side .of said conductive Arings having an angle of inclination substantially equal .to and in a direction opposite to those ferrite members .disposed on the opposite side of said conductive rings.

3, A .traveling-wave tube comprising an evacuated envelope, a slow-wave structure having a longitudinal axis and disposed within said envelope for propagating electromagnetic waves, said slow-wave structure includ- ,ing a plurality of conductive rings having apertures disposed along said longitudinal axis in register with each other, and conductive. means lying in an axial plane including said .axis and.disposed between adjacent pairs 4of said conductive rings connecting said adjacent pairs of said conductive Vrings alternately at diametrically on posed points, an electron gun disposed Within one end of said envelope for projecting an electron stream through said slow-wave structure along said axis, and an elongated ferromagnetic ferrite member disposed to one side of each of said conductive rings, said ferrite members being disposed in a plane parallel to said axial plane and having a predetermined angle of inclination with respect to a plane transverse to said longitudinal axis.

4. A traveling-wave tube comprising an evacuated envelope, a slow-wave structure having a longitudinal axis and disposed within said envelope for propagating electromagnetic waves, said slow-wave structure including a plurality of conductive rings aligned along said axis and having apertures disposed in register with each other, and conductive means lying in a first plane containing said axis and disposed between adjacent pairs of said conductive rings connecting said adjacent pairs of said conductive rings alternately at diametrically opposed points, an electron gun disposed within one end of said envelope for projecting an electron stream through said slow-wave structure, along said axis, a plurality of pairs of elongated ferromagnetic ferrite members, said members of each pair being disposed in one of two planes parallel to said rst plane on opposite sides of one of said conductive rings and each of said ferrite members having a predetermined angle of inclination with respect to a plane transverse to the longitudinal axis of said slow-wave structure, the ferrite members in one of said planes having an angle of inclination substantially equal to and in a direction opposite to that of those ferrite members disposed in the other of said planes.

5. The invention as defined in claim 3, `wherein means are provided for producing a magnetic field parallel to said longitudinal axis of said slow-wave structure and through said ferrite members to confine said electron stream and, in conjunction with said ferrite members, to produce substantially non-reciprocal attenuation of waves propagated along said slow-wave structure.

6. The invention as dened in claim 4, wherein means are provided to produce a magnetic `field parallel to said longitudinal axis of said slow-wave structure to confine `said electron stream and, in conjunction with said ferrite members, to produce substantially non-reciprocal attenuation of waves propagated along said slow-wave structure.

References Cited in the le of this patent UNITED STATES PATENTS Pierce Apr. 28, 1953 Luhrs et al. July 7, 1953 OTHER REFERENCES U S DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE 0F CQRRECTION l Patent No. 2,822,502 Samuel Sensper February 4 1958 It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let ters^\- Patent should read as corrected below.

Column 4, line 44, for "of seidu read to said line 48, for "structure propagating" read' structure for propagating y Signed and sealed this 17th day of June 1958.,

KARL H., AXLINE ROBERT C. WATSON Attesting Officer Comissioner of Patents 

